TALLAHASSEE — The group opposing a proposed constitutional amendment legalizing medical marijuana raised $2.7 million in May. Nearly all of that – $2.5 million – came from Las Vegas casino magnate Sheldon Adelson.

“We already know that this will be an expensive campaign given proponents of legalization have said they will spend whatever it takes,” said Sarah Bascom, a spokeswoman for Vote No on 2.

She said the amendment is “written so broadly that it will really mean pot for any purpose if it passes.”

The group advocating for the measure, People United for Medical Marijuana, has raised $3.1 million, most of that since January 2013. The group has spent $4.8 million; $1.9 million in loans from the firm of attorney John Morgan — major backer of the effort — has kept the group in the black.

People United has not posted its May numbers, but campaign manager Ben Pollara says it raised over $200,000 in May. Pollara blasted the $2.6 million raised by the opposition group.

“Most of that came from a casino billionaire,” Pollara said, speaking of Adelson, chairman and CEO of Las Vegas Sands. “We haven not received a dime from John Morgan since February, and have more than 3,000 contributors.”

Pollara also said the group spent $70,000 a poll in May, which drove up expenses.

Much of the group’s expenditures were to collect enough signatures to get on November’s ballot. To become law, the measure needs approval from 60 percent of voters. Most polling data shows the measure is likely to clear that hurdle.